In general, a light emission of a conventional light emitting diode (LED) is that the light emission path is normal to the light emission surface of the LED chip, and a Lambertion energy distribution fashion is presented (referring to FIG. 1A). For applications in traffic lights, illumination or other indicative signals, due to the limitation of energy distribution profile, if a plurality of LEDs are mixed optically (such as mixing of light intensity, color lights, or the like), a desired mixing result is obtained only at a selected distance from the light emission surface of the LEDs (referring to FIG. 1B). There is an ineffective distance L1 where mixing cannot be performed. However, if the lighting profile of the individual LEDs is flattened, the ineffective distance can be shortened.
Lumileds Co. announced a side emitting LED in the SID seminar in 2003. It disclosed the side emitting LED with a special package structure (referring to FIG. 2). Adopted such a structure, the side emitting LED has only a small portion of light energy (less than 10%) emits through the upper side (in a direction of a central optic axis 14 of the LED chip). Most light energy emits in lateral directions. In practical applications, this type of side emitting LED reflects the light energy which emits upwards through a mask 16 attached to the upper side thereof. Lumileds Co. also has obtained U.S. Pat. No. 6,679,621 entitled “Side emitting LED and lens” for that technique.
In U.S. Pat. No. 6,679,621, Lumileds Co. discloses a package structure such as a lens (referring to FIG. 3). It included an incident surface 10, a reflective surface 11, a first refractive surface 12 and a second refractive surface 13. The first refractive surface 12 and the central optic axis 14 of the LED chip form an angle. The second refractive surface 13 is connected smoothly to the first refractive surface 12 and a bottom surface 15. A light emitted from the LED chip enters the package structure through the incident surface 10, and emits mainly along two paths P1 and P2. The light on the path P1 enters the package structure through the incident surface 10 to the reflective surface 11, is reflected to the first refractive surface 12 by the reflective surface 11, and then is refracted by the first refractive surface 12 to exit the package structure along the path P1. The light on the path P2 enters the package structure through the incident surface 10, and directly is refracted by the second refractive surface 13 to exit the package structure along the path P2. However, the package structure shown in FIG. 3 has problems, notably:
1. As the light is divided into two optical paths, an “optical path overlap” easily occurs on boundaries of the two optical paths. As a result, an improper reflection or refraction takes place. Referring to FIG. 4, there is an optical path overlap zone α between the first refractive surface 12 and the second refractive surface 13. If the light entered the package structure through the incident surface 10 enters the overlap zone α, it directly arrives the first refractive surface 12, and the improper reflection or refraction occurs.
2. Such a package structure has a narrow portion geometrically. As a result, the structure is not strong enough.
3. The profile of the package structure has many acute angles. It tends to form stress concentration during fabrication and results in deformation. As a result, it changes optical characteristics of the package structure.